Question: What is the slope of the line tangent to $f(x) = -2x^{2}-2x+5$ at $x = -1$ ?
The slope of the tangent line is $ \lim_{\Delta x \to 0} \frac{f(x + \Delta x) - f(x)}{\Delta x}$ $ = \lim_{\Delta x \to 0} \frac{(-2(x+\Delta x)^{2}-2(x+\Delta x)+5) - (-2x^{2}-2x+5)}{\Delta x}$ $ = \lim_{\Delta x \to 0} \frac{(-2(x^{2}+2x \Delta x+\Delta x^{2})-2(x+\Delta x)+5) - (-2x^{2}-2x+5)}{\Delta x}$ $ = \lim_{\Delta x \to 0} \frac{-2x^{2}-4(x \Delta x)-2\Delta x^{2}-2x-2(\Delta x)+5+2x^{2}+2x-5}{\Delta x}$ $ = \lim_{\Delta x \to 0} \frac{-4(x \Delta x)-2\Delta x^{2}-2(\Delta x)}{\Delta x}$ $ = \lim_{\Delta x \to 0} -4x-2(\Delta x)-2$ $ = -4x-2$ $ = (-4)(-1)-2$ $ = 2$